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cmd/compile: use standard dom tree in nilcheckelim

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No need to build a bespoke dom tree here when we might
have one cached already.  The allocations for the dom tree
were also more expensive than they needed to be.

Fixes #12021

Change-Id: I6a967880aee03660ad6fc293f8fc783779cae11d
Reviewed-on: https://go-review.googlesource.com/30671
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Keith Randall 2016-10-07 10:08:10 -07:00
parent 433be563b6
commit f4e37c8ec5
1 changed files with 2 additions and 10 deletions
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12
src/cmd/compile/internal/ssa/nilcheck.go
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@ -10,15 +10,7 @@ func nilcheckelim(f *Func) {
// A nil check is redundant if the same nil check was successful in a
// dominating block. The efficacy of this pass depends heavily on the
// efficacy of the cse pass.
idom := f.idom()
domTree := make([][]*Block, f.NumBlocks())
// Create a block ID -> [dominees] mapping
for _, b := range f.Blocks {
if dom := idom[b.ID]; dom != nil {
domTree[dom.ID] = append(domTree[dom.ID], b)
}
}
sdom := f.sdom()
// TODO: Eliminate more nil checks.
// We can recursively remove any chain of fixed offset calculations,
@ -128,7 +120,7 @@ func nilcheckelim(f *Func) {
b.Values = b.Values[:i]
// Add all dominated blocks to the work list.
for _, w := range domTree[node.block.ID] {
for w := sdom[node.block.ID].child; w != nil; w = sdom[w.ID].sibling {
work = append(work, bp{op: Work, block: w})
}